Since the public mobile radio systems were introduced in the late 1970s and early 1980s, several “generations” of mobile radio communication systems have evolved in different parts of the world. First generation (1G) systems used analog frequency modulation at the radio and digital control of the network. Second generation (2G) systems are based on Time Division Multiple Access (TDMA). An example of a 2G system is the Global System for Mobile Communications (GSM). Work is ongoing in third generation (3G) systems based on Wideband Code Division Multiple Access (WCDMA). An example of a 3G system is a Universal Mobile Telecommunication System (UMTS).
Third generation systems are backward compatible with other types of radio systems—like GSM—so that multimode User Equipment (UE) can obtain service from both 2G and 3G systems. This requires that the multimode UEs and the 2G and 3G infrastructure all support inter-system handover from a cellular that employs one type of radio access technology to another cellular system that employs a different type of radio access technology, e.g., from GSM/TDMA to UMTS/TDMA. Commonly assigned U.S. patent applications Ser. No. 09/286,472, filed on Apr. 9, 1999 and entitled, “Inter-System Handover—Generic Handover Mechanism,” describes one mechanism for accomplishing such intersystem handovers, the disclosure of which is incorporated herein by reference.
In addition to coordinating inter-system handovers, network operators may share their network in order to extend network coverage and provide other extended network services to their respective subscribers. Shared networks may be geographically split or they maybe commonly shared. In a geographically split network, each operator covers a different geographical area with its respective network. Consider an example where two cellular network operators A and B share each other's network to provide their subscribers with cellular coverage over an entire country. Operator A's network may cover one half of the country, and operator B's network covers the other half. Network sharing allows both network's mobile subscribers to have service throughout the entire country. A problem arises when the two networks overlap, e.g., in the middle of the country. In that overlapping area, service can be provided by either operator's network. Naturally, each operator would like its subscribers to use its network in this overlap area, with access to the other operator's network restricted or prohibited. In other words, each operator wants to service its own subscribers using its own infrastructure whenever possible.
In one likely shared network example, a UMTS is shared by network operators A, B, and C, and each operator has its own GSM network overlapping the UMTS and the other GSM networks. The problem arises when a user equipment (UE) is leaving the UMTS network area that is not overlapped by any of the GSM networks and must be handed over into an area where the UMTS and the three GSM networks overlap. In this situation, it would be desirable to restrict which GSM network cells are possible candidates for handover. For example, if the UE is a subscriber of operator A, it would be desirable to restrict the GSM handover candidate cells for that UE to those belonging to operator A's GSM network. A GSM cell belonging to operator B or C should only be selected if no cell in A's network is available.
One approach to solving this problem is to provide shared network access/restriction information to every network node involved in handover decision making. The difficulty with this approach is the need to distribute large volumes of shared network area (SNA) information with high frequency to many nodes. Such SNA access data must be sent to the radio access network at every call setup and must also be included in every handover/relocation message. This frequent SNA signaling containing substantial amounts of SNA data requires considerable bandwidth. In addition to significant bandwidth resources being consumed, signaling protocol messages typically have maximum lengths so there may not even be sufficient room to carry the necessary SNA information.
The present invention solves these problems with distributing SNA information using indicators that represent the SNA information. SNA information for a first group of first network mobile subscribers is mapped to a first indicator. Similarly, second shared access network information for a second group of second network mobile subscribers is mapped to the second indicator. Those mappings are established in a core network node and sent to radio network nodes involved in call connection setup and/or handover. The radio network nodes store these mappings for future use.
When a call connection is being set up (or soon thereafter) with one of the first network mobile subscribers, a core network node sends the first indicator to the radio network node handling the connection set up. That radio network node uses the first indicator to determine from its stored SNA table the network access restrictions for this subscriber. The shared network access restriction information is not sent—only the indicator.
If a handover is requested for the call connection from the first radio network node to a second radio network node, the first indicator is sent to the second radio network node. The second radio network node uses the first indicator to determine from its SNA mapping the network access restrictions for this subscriber. Based on the determined network access restrictions, the second radio network node selects an appropriate cell for the handover.
Thus, in shared network situations, using SNA indicators conserves resources every time a call is set up and every time a call is handed over. Sending only the SNA indicator rather than all of the SNA information reduces signaling complexity and volume. This allows network operators to efficiently control which network cells are permitted as viable handover candidates.